The data that is supplied on the platform is proprietary information provided by Refinitiv.
For Over or Under Valued percentage, please see below the calculation. A screenshot for CBA is attached as an example.
Over/Under Valued Percentage = (Mean - Last Close Price) / Last Close Price) * 100
I.e. With CBA (91.02 - 117.12) / 117.12) * 100 = 22.3%
Mean price can be obtained from the Price Forecast section on the Forecast page, as per the screenshot.
Items to note, The value isn't updated at the same time as the close price. The value also doesn't change during the day, so should a price jump up or down, it doesn't reflect that change either.